Adding WMS services is described in the 'Web Map Services' topic in the documentation.
You have to know the URL to the WMS, and the list of layers the WMS supports.
Dim wms As WmsLayer = New WmsLayer("http://terraserver-usa.com/ogcmap6.ashx", New AspMap.Rectangle(-122.47, 37.87, -122.18, 37.73))
wms.AddLayer("UrbanArea") ' internal WMS layer
map.ImageFormat = ImageFormat.Png
map.ImageOpacity = 0
For information about a particular WMS, please contact the provider of the WMS.